Effect of cooling rate, extender type, and storage temperature on chilled sperm quality and pregnancy rate in Kail sheep

Abstract

This study aimed to evaluate how cooling rates, extender type, and storage temperatures affect sperm quality and fertility in Kail sheep. In the first experiment, pooled semen collected from 5 adult Kail rams was extended with a Tris-based extender and divided into three aliquots. The temperature was reduced from 37 °C to 5 °C in 30 min (rapid cooling), 60 min (moderate cooling), and 90 min (slow cooling). In the second experiment, pooled semen was extended with three extenders: Tris, skim milk, and sodium citrate-based, and stored at 5 °C and 12 °C for three days. In the third experiment, ewes (n = 63) were synchronized for estrus using a progestin-based protocol, and fixed-time cervical insemination (FTCI) was performed at 48 h (n = 25) and 60 h (n = 38) after the sponge removal using semen extended in Tris-based extender. Results revealed that slow cooling rates had less (P < 0.05) detrimental impact on sperm motility and kinematics when compared to both moderate and rapid cooling rates. Moreover, semen extended with Tris-based extenders had a higher (P < 0.05) percentage of motile, progressive motile, rapid progressive, and medium progressive motile sperm compared to extenders containing skim milk and sodium citrate. Storage of semen at 5 °C better preserved sperm quality compared to 12 °C. Storage duration exerted a negative influence (P < 0.05) on sperm quality across all three extender types. The overall 55.5% pregnancy rate was achieved. The season of insemination had a significant impact while the timing of insemination did not influence the pregnancy rate. In conclusion, sperm quality is better preserved when semen is stored at 5 °C and subjected to a slow cooling rate using a Tris-based extender, and the success of FTCI is contingent upon the season of insemination in Kail sheep.